Belt

ABSTRACT

A continuous variable transmission belt includes a set of nested metal rings, the set interacting with transverse elements provided slidably along the set, and the rings of the set being accommodated with small mutual play between each pair of adjacent rings, where for at least the majority of the pairs of adjacent rings the nominal value of the play is zero. The innermost and outermost rings having an elasticity modulus significantly lower than the intermediate rings.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of co-pending application Ser. No.10/088,118m filed on Mar. 15, 2002, the entire contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a belt for use in a ContinuouslyVariable Transmission.

DESCRIPTION OF RELATED ART

Such a belt is generally known, more in particular from the U.S. Pat.No. 3,720,113. Belts satisfying the described characteristics mentionedin this document are known in practice, and prove to performsatisfactorily. The set of rings shown by such belts will be describedas adjacent rings, alternatively denoted hoops or strips, and adjacentmeaning directly adjacent, in other words such that mutual abutment maytake place between adjacent rings in a set.

Despite the known belt is at present commercially available for morethan a decade, and is technically known for even many more years, it isin practice still found that the endurance time of belts may still besignificantly improved.

SUMMARY OF THE INVENTION

It is therefor an object of the invention to enhance durability of theknown belt while maintaining and preferably improving the powertransmitting capacity of the known belt. According to the presentinvention this may in a surprisingly simple manner be achieved by thatdescribed below.

A problem underlying the invention is how to determine one ore morespecific features of a belt related to the endurance thereof. One suchfeature is suggested by U.S. Pat. No. 4,579,549, teaching that theinnermost ring, alternatively denoted hoop, is subjected to the biggesttensile stress of all the hoops. Decrease of tensile stresses of theinnermost hoop is mentioned to enhance the service life thereof andtherewith of the belt. For achieving such, the document furtherindicates the hoops of a set to be “superimposed with no clearancebetween abutting hoops”. This indication is in the document explained tomean that each of the hoops has an outer circumferential diameteradapted to be equal to, or larger than, an inner circumferentialdiameter of an abutting outer hoop. The technical effect of such measureis suggested to be that the tensile stresses of the hoops increase withthe increase in diameter thereof. This measure is further explained tobe found as an inverse or opposite effect found at prior art belts“which have clearances of 30 μm between abutting hoops”, and which priorart belts featured a decreasing tensile stress with an increasingdiameter of the respective rings. It is here remarked that said latterprior art feature fits the teaching of above mentioned earlierpublication U.S. Pat. No. 3,720,113 in that practically no play couldinclude a play of 30 μm for as far as belts of a dimension within therange for regular automotive application are concerned.

A confirmation of the teaching of above mentioned publication U.S. Pat.No. 4,579,549 is provided by the recent publication of Japanese patentabstract No. 10169719 of application No. 08332187. In this publicationthe rings of a set are indicated to require a likewise so called minusclearance or, alternatively denoted, a negative play.

Both abstract and U.S. Pat. No. 4,579,549 suggest the characteristic ofplay between rings of a set to be important in relation to life time ofa belt. These documents however provide a measure effecting aconfusingly inverse effect on distribution of belt tension in the ringsof a set.

As to U.S. Pat. No. 3,720,113, when interpreted with the teaching ofU.S. Pat. No. 4,579,549, pointing to play between rings, it is foundthat rings of the first known belt “are super imposed with practicallyno play.” For a practical implementation and for use as a starting pointfor improvement, this indication is too vague. An obvious interpretationof this teaching however, would be to utilise the inverse expression,indicating that the rings are superimposed with some play, be itpractically absent. Belts of this nature are likely to show thedistribution of tensile stresses conforming to the distribution shown asprior art in U.S. Pat. No. 4,579,549, i.e. will have highest tensilestress at the innermost ring. Adopting the solution of the latter U.S.Pat. No. 4,579,549 document, it is unsatisfactory found that thissolution leads to still one weakest ring, however, now located at theoutermost side of a ring set.

The present invention overcomes the drawbacks of all prior art byprescribing a play of nominal value zero. In this way an evendistribution of ring stress over at least the majority of the rings of aset is effected, realising a balanced transfer of tensile stress betweeneach relevant ring. Moreover, the level of tensile stress so realised inany ring of a set is significantly lower than that in the ring withhighest tensile stress in any of both known solutions. It will be foundthat with a belt according to the invention the life time of a belt isincreased to such extend that durability may with impunity be exchangedagainst the level of torque to be transmitted, e.g. the effect may beutilised by applying the essentially same belt in environments withhigher torque to be transmitted. Should all pairs of rings beaccomodated with play of nominal value zero, it will be found that lifetime is enhanced in respect of belts with any above mentioned prior artmeasure, not in the last instance because belts are in practice found tofail either through failure of the innermost ring or through failure ofthe outermost ring.

In order to reproduce the above effect in a sufficiently consistent andreliable manner a favoured embodiment according to the inventionrequires that the nominal value of zero is realised by a tolerance of0.00005 times the outer diameter of the inner ring of a relevant pair ofrings, plus or minus of the diameter. The technical effect of thismeasure according to the invention is that the differences of lifetimeeffect will remain within an accepted bandwidth for technicallyequivalent belts. In further detail of this effect, it will be foundthat that no significant difference in life time can be remarked as aconsequence of this measure, since the effect hereof is that the spreadof life time consequence of this measure will normally remain within thenatural life time spread caused by metal fatigue.

Yet another preferred embodiment of the invention requires the mutualplay between the innermost pair of adjacent rings is of negative value.It is acknowledged by the invention that the innermost ring of a set, asdescribed by U.S. Pat. No. 4,579,549, “is subjected to both tensileforces and frictional forces”. However, as indicated below, the measuresubsequently taught by said publication is rejected. Rather, thefavoured embodiment applies the idea underlying the present invention tosolve the problem of the first ring, i.e. to take account of the tensioneach ring is individually subjected to. Combining this idea with theinsight underlying the invention that the innermost ring is subjected tocertain forces specific thereto, it was found according to this specificaspect of the invention that the tensile stress should be keptrelatively low in order to keep the total level of stress in theinnermost ring at a level conforming to the level in remainder of therings of a set. In this respect it was recognised that the frictionalforce following from interaction between the innermost ring and thetransverse elements as mentioned in U.S. Pat. No. 4,579,549, whencompared to frictional force resulting from ring-ring interactions ishigh, so that an additional frictional force should be calculated withfor the innermost ring. At the innermost ring it should further becalculated with so-called Herze tensions resulting from element-ringcontact. A favoured manner of keeping the level of tension in theinnermost ring at the level of the in-between rings of a set is,according to the invention, to reduce the tensile stress by providingsome negative play for the innermost ring only.

In a further advancement of above measure directed to the play of theinnermost ring specifically, the invention is further characterised inthat the outermost diameter of the innermost ring is of a value (1−Z)times the inner diameter of the adjacent ring, Z being of a valuesmaller than 0.0008. A technical effect of the so specificallyidentified range is that the reliability and consistency of the effectof the measure related to the innermost belt is increased, while takinginto account further sources of tension specific to the innermost belt,including e.g. so called Herze tensions originating from theelement-ring contacts. In this respect the value of greater than 0.0001effects yet a further enhancement. It will be found that, although theparameter Z to some extent varies with the application of a relevantbelt, a belt is stressed in conformance with the in-between ring, thushaving a conforming life time, when the parameter Z is kept in the abovethe range.

A further specific aspect of the invention relates to a belt wherein themutual play of the outermost pair of adjacent rings is of positivevalue. The technical effect hereof is that compensation is provided fortension sources other than tensile stress, specific to the outer rings,such that the total tension in the outer ring may be brought intoconformance with, i.e. will not be higher than, the tension in thefurther rings of a set. An insight underlying this aspect of theinvention is that a tension source specif to the outer rings is causedby subjection to intense contact with transverse elements, i.e. with theboundary opposite to the so-called saddle part, at the instant where thebelt should escape out of the pulley in which it is to be operated.Since the elements are clamped between the sheaves of a pulley, theytend to rotate therewith. For transmitting force to the other puleyhowever, the belt and the elements should cross to the other pulley.Thus the elements are pulled out of the sheaves at the instance ofleaving the pulley, thereby causing intense contact between theso-called ear part of a transverse element and the outermost ring. In afurther development of this aspect the inner diameter of the outermostring is of a value (1+Y) times the outermost diameter of the adjacentring, Y being of a value smaller than 0.0004 and preferably greater than0.00005. When the values of this specific range are followed thetechnical effect indicated at the range for the innermost ring will befurther enhanced.

A particular aspect of the invention is characterised in that thethickness of one or both of the innermost and the outermost ring of theset is significantly by less than the nominal thickness of in betweenrings of the set. The invention therefor also relates to a belt for usein a continuously variable transmission, in particular for automotiveapplication, comprising at least one set of nested metal rings, the setinteracting with transverse elements provided slidably along the set,and the rings of the set being accommodated with small mutual playbetween each pair of adjacent rings, whereby the thickness of one orboth of the innermost and the outermost ring of the set is significantlyless than the nominal thickness of in between rings of the set. Withsuch a measure the invention provides an alternative means of realisingan evenly distributed tension level over the rings of a set. The insightutilised in this invention is that a smaller thickness realises a lowerbending stress in the relevant ring thereby lowering the tension levelin the innermost and/or outermost ring, allowing the relevant ring toreceive tension from sources specific therefor, without penalty inregard of life time.

Yet another particular aspect of the invention relates to the measurewherein the material composition of at least one of the innermost andthe outermost ring of the set significantly differs from that of the inbetween rings of the set, such that the elasticity modulus thereof issignificantly lower than that of in between positioned rings. Theinvention therefor also relates to a belt, for use in a continuouslyvariable transmission, in particular for automotive application,comprising at least one set of nested metal rings, the set interactingwith transverse elements provided slidably along the set, and the ringsof the set being accommodated with small mutual play between each pairof adjacent rings, whereby the elasticity modulus of one or both of theinnermost and the outermost ring of the set is significantly less thanthe nominal thickness of in between rings of the set. With such ameasure get another alternative for realising an evenly distributedtension over all rings of a set is realised. The technical effect iscomparable to the preceding alternative.

In a further elaboration of the latter aspects the value for thicknessand elasticity modulus of the innermost and the outermost ring is atleast twenty percent (20%) less than the average value of the parametersat the in-between rings. When the values of this specific ranges arefollowed, the technical effect in durability and torque to betransmitted, indicated a.o. at the range for the innermost ring, will befurther enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now further be explained by way of examples given inthe accompanying drawing wherein:

FIG. 1 is a schematic illustration of the belt the present inventionrelates to, together with the transmission wherein it is to be operated;

FIGS. 2 and 3 by way of cross sections indicate transverse elements fortwo of many possible types of belt that may be provided with thefeatures of the invention;

FIG. 4 is a side elevation of the cross elements according to FIGS. 2and 3;

FIG. 5 is a plot indicating the level of tension for each ring in a setof rings of a belt, both for a belt according to prior art and for abelt according to the invention, and

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows schematically a continuous variable transmission (CVT)suitable amongst others for automotive application, with a conveyor belt1, made up of a carrier in the form of a nested set of endless thinbands 2, otherwise denoted rings 2 and a multitude of separatetransverse elements 3, otherwise denoted blocks 3. The elements 3 arearranged freely slidably along the carrier 7 in an endless, virtuallycontinuous series. The carrier 7, alternatively denoted support and ringset is composed of a number of the in endless bands, alternativelydenoted loops or rings. For operational application the belt 3 runswithin the V-shaped groove of the pulleys 1 and 2 with steplesslyvariable diameter. Its elements 6 are provided with inclined contactfaces for contacting the sheaves 4 and 5 of the pulleys. The pulleys 1and 2 are provided on shafts P and S respectively. When pinchedsufficiently strong between the sheaves of a pulley 1, 2 the belt 3transmits force from one rotating pulley to the other. The elements 6,as seen in cross section preferably have a lower part of which at leastone principle side is inclined relative to the upper part at the sameside, so that the element 6 becomes thinner towards the side directed tothe inner side of the belt. Such a continuous variable transmission isknown per se. The elements 6 further are provided with generallyslightly convexely shaped contact faces also denoted saddles forcontacting the support 7, in particular the innermost band thereof.

In operation the belt, through the rotation of a driving pulley passes atrajectory with upper and lower predominantly straight parts between thepulleys, and with first and second predominantly circular trajectories,where the belt is clamped by the sheaves of a pulley. In one of thestraight parts each time, between the pulley clamped circulartrajectories of the belt, the carrier 7 may be subjected to highesttensile forces. In practice the belt in one straight part may becomesomewhat buckled due to the elements pushing against each other, therebyvirtually forming a metal rod between said pulleys, and having thetendency of splashing apart. This tendency however, is counteracted bythe carrier 7, which according to the invention in the push is may besubjected to relatively high tensile stresses. However, high tensilestress may depending on the state of the belt, also occur at theopposite straight part where the belt, i.e. the carrier 7, is subjectedto high pulling force.

FIGS. 2 and 3 show possible embodiments of a transverse element 6. FIG.2 depicts a so called single package element having a central opening 13for receiving a ring package, alternatively denoted set of rings 7. Theopening is bounded to its upper side by a removable closure element 10,e.g. embodied by a pin. The pin 10 is received by opening 11 and 13respectively, provided in upwardly parts of the element defining theopening 13. In a lower part thereof, each element is provided with sidefaces 8 for contacting the side faces the respective sheaves of a pulleyin a matching plane.

FIG. 3 depicts an embodiment for receiving dual ring sets 7, for whichpurpose two ring receiving slots 14 are provided. Each slot 14 areprovided. Each slot 14 has a lower saddle part and an upper boundaryprovided through an upper T-shaped element part.

FIG. 4 shows the contact face 8 to be roughened in the depicted example,embodied by rills 16 and grooves 15, so as to allow passage of a coolingmedium such as transmission oil. FIG. 4 further shows the elements 6 tobe relatively thin, and to have a lower element part declining inthickness towards its lower end so as to allow a belt to be bend whenpassing a pulley trajectory. Due to a tension within a set of rings theinnermost ring at least the part thereof pressing a trajectory within apulley is in stiff contact with the so called saddle part of an element,i.e. the lower element part of the spaces 13 and 14 for ring sets in theFIGS. 2 and 3 respectively.

FIG. 5 is a figurative representation of the highest possible tension Soccurring in any above mentioned parts or trajectories passed duringoperation of the belt, plotted for each ring N of a ring set, hereprovided with 10 rings. Number 1 in the plot stands for the innermostring of the set, whereas No. 10 stands for the outermost ring. A similarplot can be made up for any number of rings in a set. The broken line inFIG. 5 represents a commercially available belt provided withpractically no play, i.e. with at least some play between the rings. Thesolid line represents the tension in each ring of a belt according tothe present invention in which the play between the ring has, asexpressed in technical terms, a nominal value of zero. In commonlanguage this means that an inner ring of any pair of rings of a set mayhave some play relative to the outer ring, or may be somewhat longerthan the inner diameter of the outer ring. In technical terms thesestates are denoted positive and negative play respectively. The notionnominal further includes that the average value of plays of a givennumber of pairs of rings is zero. In technical sense this zero valueincludes a certain margin. In the construction a favourable embodimentof the margin would be 0.00005 times the outer diameter of an inner ringof any pair of a set in each direction, i.e. plus or minus of the outerdiameter.

1. Belt (1) for use in a continuously variable transmission, comprising:at least one set (7) of nested metal rings (2), the rings (2) of the set(7) being accommodated with small mutual play between each pair ofadjacent rings (2); and transverse elements (3, 6) provided slidablyalong the set (7), wherein, the set (7) interacts with the transverseelements (3, 6), and a thickness of one or both of an innermost ring (2)and an outermost ring (2) of the set (7) is significantly less than thenominal thickness of in-between rings (2) of the set (7) intermediatethe innermost and outermost rings (2).
 2. Belt (1) according to claim 1,wherein the thickness of said innermost ring (2) or said outermost ring(2) is at least twenty percent (20%) lower of the average value of thethickness of the in-between rings (2).
 3. Belt (1) according to claim 1,wherein for at least the majority of said pairs of adjacent rings (2), asum of positive amounts and negative amounts of play between said pairsof adjacent rings (2) is zero.
 4. Belt (1) according to claim 1, whereina nominal value of said play is zero realized by a tolerance of 0.00005times an outer diameter of the inner ring (2) of a relevant pair ofrings (2), plus or minus of said diameter.
 5. Belt (1) according toclaim 1, wherein said mutual play between the innermost pair of adjacentrings (2) is of negative value.
 6. Belt (1) according to claim 5,wherein the outer diameter of the innermost ring (2) is of a value 1−Ztimes the inner diameter of the adjacent ring, Z being of a valuesmaller than 0.0008.
 7. Belt (1) according to claim 6, wherein Z is of avalue greater than 0.0001.
 8. Belt (1) according to claim 5, wherein themutual play of an outermost pair of adjacent rings (2) is of positivevalue.
 9. Belt (1) according to claim 8, wherein the inner diameter ofthe outermost ring (2) is of a value 1+Y times the outer diameter of theadjacent ring, Y being of a value smaller than 0.0004.
 10. Belt (1)according to claim 9, wherein Y is of a value greater than 0.00005. 11.Belt (1) according to claim 1, wherein said mutual play of an outermostpair of adjacent rings (2) is of positive value.
 12. Belt (1) for use ina continuously variable transmission, comprising: at least one set (7)of nested metal rings (2), the rings (2) of the set (7) beingaccommodated with small mutual play between each pair of adjacent rings(2); and transverse elements (3, 6) provided slidably along the set (7),wherein, the set (7) interacts with the transverse elements (3, 6), anda material composition of at least one of an innermost ring (2) and theoutermost ring (2) of the set (7) significantly differs from that of thematerial composition of in-between rings (2) of the set (7) locatedintermediate the innermost and outermost rings (2) such that theelasticity modulus of the at least one of the innermost and theoutermost rings is significantly lower than the elasticity modulus ofin-between rings (2).
 13. Belt (1) according to claim 12, wherein theelasticity modulus of said innermost and said outermost rings (2) is atleast twenty percent (20%) less than the average value of the elasticitymoduluses of the in-between rings (2).
 14. Belt (1) according to claim12, wherein for at least the majority of said pairs of adjacent rings(2), a sum of positive amounts and negative amounts of play between saidpairs of adjacent rings (2) is zero.
 15. Belt (1) according to claim 12,wherein a nominal value of said play is zero realized by a tolerance of0.00005 times an outer diameter of the inner ring (2) of a relevant pairof rings (2), plus or minus of said diameter.
 16. Belt (1) according toclaim 12, wherein said mutual play between the innermost pair ofadjacent rings (2) is of negative value.
 17. Belt (1) according to claim16, wherein the outer diameter of the innermost ring (2) is of a value1−Z times the inner diameter of the adjacent ring, Z being of a valuesmaller than 0.0008.
 18. Belt (1) according to claim 17, wherein Z is ofa value greater than 0.0001.
 19. Belt (1) according to claim 16, whereinthe mutual play of an outermost pair of adjacent rings (2) is ofpositive value.
 20. Belt (1) according to claim 19, wherein the innerdiameter of the outermost ring (2) is of a value 1+Y times the outerdiameter of the adjacent ring, Y being of a value smaller than 0.0004and greater than 0.00005.